The Question:

What is the longest river in the world and how long is it and
through what countries does it flow?

The Answer:

The Nile is the longest river in the world. It's 4,160 mi (6,695
km) long from its remotest headstream, the Luvironza River in Burundi,
central Africa, to its delta on the Mediterranean Sea, NE Egypt. The
Nile flows northward and drains c.1,100,000 sq mi (2,850,000 sq km),
about one tenth of Africa, including parts of
Egypt, Sudan,
Ethiopia, Eritrea,
Kenya, Uganda,
Rwanda, Burundi,
Tanzania, and Congo
(Kinshasa). Its waters support practically all agriculture in the most
densely populated parts of Egypt, furnish water for more than 20% of
Sudan's total crop area, and are widely used throughout the basin for
navigation and hydroelectric power.